…continuedFreeware from Sky & Telescope
In the Telescope Techniques department in the July 2002 issue of Sky & Telescope (PDF of article) Glenn LeDrew showed how to make a pair of right-angle, correct-view binoculars. The article features a DOS program called Binoplan that calculates the spacing of the various optical elements and shows on-axis and off-axis vignetting. You can download it here. Be sure to select "Save program to disk" when prompted, and unzip the file using an uncompressing utility, such as 7-zip or StuffIt Expander.